Fail proof radiation monitor and alarm circuit



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Ill/Ill existence of an abnormality in a monitored region.

FAlL PROGF RADTATTGN MGNITQR AND ALARM CKRCUET Wallace Jones, Saltsburg, Pat, assignor to Nuclear Materials and Equipment Corporation, Apollo, Pa, in corporation of Pennsylvania Filed Tan. 12, 1%0, Ser. No. 2,921

14 Claims. (Cl. 250-833) 1 This invention relates to the signalling art and has particular relationship to the detection and signalling of the In its specific aspects this invention concerns itself with the detection and signalling of the presence of excessive radioactivity in a protected region and this invention is peculiarly tied in with radioactivity and the character of detection and signalling which radioactivity demands. In its broader aspects this invention is applicable to detection generally, for example to burglar alarms and the like.

The detection of radioactivity is of such vital importance that the United States Government has promulgated These reguobject of this invention to provide a highly reliable radiov activity alarm system. v

In addition the code demands that the apparatus be jam proof and it is another object of this invention to provide an alarm system which shall be jam proof. It is an ancillary object of this invention to provide a jam-proof sensing device for a radioactivity alarm system which shall operate at a relatively low voltage. Another ancillary object of this invention is to provide a sensing unit for a radioactivity alarm system which shall have relatively long life in service.

The reliability demand on the alarm system imposes the requirement that the system shall be automatically selftesting and shall test itself at reasonable intervals, for example, every hour. A complete self-test demands that the overall system from the radioactivity pick-up unit through the alarm device be tested. The sounding of the main alarm during test would alert the area when sounded and the resulting disorganization of the personnel is undersirable. In addition, the repetition of the main alarm signal at relatively short intervals is highly disagreeable. It is, an important object of this invention to provide a self-testing or self-checking method for a-radioactivity detecting and signal system in the practice of which the overall system shall be completely tested or checked but which shall not produce the disorganization and discomfort of personnel produced by repeatedly sounding the main alarm.

It is another object of this invention to provide an alarm system embodying facilities for self-testing without disorganization of, and discomfort to, personnel.

In accordance with this invention in one of its specific aspects a jam-proof alarm system is provided, the heart of which is a novel radioactivity sensing device. This device includes the usual pick-up element such as a Geiger- Mueller counter which produces current pulses in response to the incidence of radioactive radiation for example gamma rays. The pulses are integrated and if repeated at a critical rate actuate a luminescent element having a critical break-down voltage. The luminescent element actuates photorsensitive means which enables the main alarm.

alarm is enabled but its sound level is reduced so that it is heard only by the monitoring operator. The high sound-level portion of the alarm unit is at the same time tested by sounding a non-alarming signal such as chimes. Both the alarm and the non-alarming signal may be recorded on a drum or a tapewhich may be reproduced to produce the signals. 7

The novel features considered characteristic of this invention are described generally above. This invention itself both as to its organization and to its method of operation together with additional objects and advantages thereof will be understood in detail from the following description of specific embodiments taken in connection with the accompanying drawing in which:

FIGURE 1 is a schematic showing a preferred embodiment of this invention; 7

' FIG. 2 is a view in section of a light responsive current converter in accordance with this invention which is particularly useful in apparatus of the type shown in FIG. 1 but may have other uses;

FIG. 3 is a schematic showing a detecting device in accordance with a modification of this invention; and a FIG. 4 is a schematic showing an embodiment of this invention including the light-responsive current converter in accordance with this invention.

Desci'ipti0n-El G. 1

The apparatus includes hot conductor LH and ground conductor LG which. supply single-phase alternating current and may be energized from a commercial single-phase supply through the usual fuses, disconnects or circuitbreakers (not shown). Preferably LH and LG should be energized from a high reliability supply through a regulator (not shown). Typically the voltage derivable from LH and LG should be volts 1 0.5 volt. Directcurrent potential for the Detecting Unit may be derived from the conductors LH and LG through a suitable rectifier (not shown). This potential is of relatively high magnitude typically of the order of 700 to 1500 volts. The negative pole of this direct-current supply is ground, the potential of the ground conductor LG. The potential for the Detecting Unit is derivable through a voltage divider RVl which permits the potential to be set at the desired magnitude between 700 and 1500 volts.

Direct-current potential for the Main Alarm Control Unit may also be derived from the conductors LH and LG through suitable rectifiers (not shown). These potentials include a higher anode potential 5, typically of the order of 104 volts, for energizing the thyratron TU of the Main Alarm Control Unit in the event of an actual alarm, a lower anode potential 7ftypically of the order of 70 volts, for energizing TU during automatic test, and a negative bias potential 9 of the order of -8 volts for biasing TU to non-conductivity during standby. These potentials are also referred to ground (the potential of LG).

In addition, there is an emergency supply a storage battery BA, which typically may be of the six-volt type.

' During standby BA may be charged from conductors LH and LG through the charging rectifier and a regulator (not shown).

The apparatus also includes an alarm conductor ALA and an automatic test conductor ALT. Conductor ALA is energized from LH during an actual alarm and con 3 ductor ALT during test. Conductor ALT is connected to the conductor LG through the solenoid 'SOI'which actuates the Test Radiation Source.

The Detecting Unit includes a pick-up device, such as a Geiger-Mueller counter GM having anode 11 and a cathode 13. This Unit also includes an integrating network IN and a light-responsive potential converting device. The network IN includes a capacitor C, which typically may have a capacity of the order of .1 microfarad shunted by a high resistor RE2 which typically may have a resistance of about 100 megohms. The lightresponsive potential converting device includes a light emitting discharge device GLI and a light-responsive device PH. The network IN isconnected across GLI.

In accordance with this invention in one of its specific aspects it is essential that the device GLI be of the abrupt type; that is, GLI remains non-conducting so long as the potential across C (IN) is below a critical magnitude but becomes conducting whenthis critical magnitude is exceeded. The light-responsive device PH is mounted adjacent the device GLI so that any light from GLI will impinge on the light-sensitive surface of PH.

A novel converter in accordance with this invention is shown in FIG. 2. This converter includes a tube 21 preferably composed of an opaque insulator such as a phenolic condensation product. Near one end of the tube 21 a cadmium sulfide crystal PHS and a small glow discharge device GLI are mounted. Conductors 23 and 25 are connected across the crystal PHS. The device GLI, the crystal PHS and the conductors 23 and 25 may be secured in the tube'21 in any convenient manner. In a typical case the tube 21 has an inside diameter of about one-quarter inch and is about 1V2 inches long. The electrodes 27 and 29 of GLI may be so spaced and the gas in GLI may be such that GLI breaks down at a precisely determinable critical voltage. Ina typical case this voltage is about 57 volts. The crystal PHS is highly sensitive and the device GLI emits abright light so that the converter shown in FIG. 2 is highly sensitive.

The adjustable arm 31 of divider RVI is connected to one terminal of the network IN through resistors RE2 and RE3 which typically may be of 1 megohm; the other terminal of IN is connected to the anode 11 of the tube GM through a resistor REl which typically may also be l megohm. The cathode 13 is connected to ground (LG). A meter ME may be selectively connected across RE3 to measure the current flowing through RE3 orthe voltage across RE3.

When radioactive radiation impinges on GM, pulses of current flow in circuit 31, RE2, RES, IN, 'REl, 11, 13 and ground. Capacitor C is then charged. If the radiation is small, the pulses are so spaced that the charge on C is on the whole dissipated through RE2 during the intervals between pulses. If the radiation is large, the pulses build up a large potential on C whichcauses GL I to break down and to energize PH. The communication between GLI and PH is by light radiation so that these may be insulated from each other and GLI and the parts connected to it may be at ahig'h potential while PH and the parts connected to it are at a low potential.

The Main Alarm Control Unit includes a thyratron TU which-typically may be a 2D21 and which has an anode 41, a cathode 43 and a control electrode 45. This unit nected to the lower anode supply (70 volts) in circuit 7,

TERa, CR, 41, 43, LG. The grid 45 is connected to the negative pole 9 of the bias through a grid resistor RE4, typically of the order of 33,000 ohms and a bias resistor RES, typically of the order of 100,000 ohms. The photo sensitive device PH is connected between the junction J of RE4 and RES and pole 5 or to pole 7 depending on the condition of relay TER.

During standby the bias 9 maintains TU non-conducting. When GLI in the Detecting Unit is energized, energizing PH, and driving I electrically positive, TU conducts actuating CR. Since TU is energized from a directcurrent supply (5 or 7), it remains conducting until disconnected from the supply. An indicator lamp 51 may be connected across the coil of CR through resistor RE6 to indicate actuation of CR.

Contact CRa when closed on actuation of relay CR energizes a system of signal lights to provide a visual alarm. Contact CRb connects a lamp 53 between the automatic test conductor ALT and LG through a resistor RE7. The lamp 53 indicates when the alarm conductor ALT is energized. CRc energizes the alarm conductor ALA when CR is actuated. The test conductor ALT is adapted to be energized through contacts TERd and CRd.

The Alarm Unit includes a drum having an alarm sound track and a non-alarming sound track such 'as chimes or pleasant music, impressed thereon. These tracks may be magnetically recorded or may be perforations or other impressions and may be picked up by the usual pick-up heads 61 and 63 respectively when the drum is rotated by motor M1. The motor M1 is connected be tween the alarm conductor ALA and LG and is energized when ALA is energized. The drum is then rotated and the sound tracks advanced for reproduction.

The Alarm Unit also includes a high-power-output audio amplifier AHG and a low-power-output audio amplifier ALG. The output of the amplifier AHG is connected to sound reproducers HOA distributed in thc.pr0- tected area where they can be readily heard by personnel. The output of the low-power-output amplifier ALG is connected to a test reproducer HOT or horn or to earphones. This reproducer HOT is positioned where it can be heard only by the attendant assigned to service the apparatus.

During standby the head 61 is connected to the input-of AHG through back contact ARb ofa selector relay AR in the Self-Testing Unit and head 63 is connected to the input of ALG through contact ARd. If the Detecting Unit responds during standby, the alarm signal is reproduced loudly on HOA and personnel is warned. The attendant hears the alarm signal from HOA and the non alarming signal and is also warned. A tendency on the part of AR to stick would then not alfect the efficiency of the alarm.

Head 63 is adapted to be connected to the input of AHG through ARc and head 61 to the input of ALG. When AR is actuated the non-alarming signal is reproduced loudly on HOA and the alarm signal is reproduced on HOT for the attendant who can determine from the signal if the system is operating properly.

The Alarm Unit also includes a Secondary Alarm which signals in the event of a commercial power failure or on the failure of the Self-Testing Unit to operate within a predetermined time interval after it is actuated. This unit is adapted to be energized from the battery BA either through back contact ARla of a power failure relay AR or through the front contacts ARZa of a timer relay in the Self-Testing Unit. The relay ARI is maintained actuated during standby from the supply'S, which in turn derives its power from LH. In the event of a power failure either at LH 'or in supply 5, ARI is deenergized and the Secondary Alarm is actuated through ARla. The Secondary Alarm is also actuated through ARZa if ARZ times out before a test signal is produced from HOA and HOT.

The Self-Testing Unit in addition to the relays AR, AR2, TER, and RA and solenoid 801, includes the timer T, and the timer relay AR3. The timer T includes,

' alarm but not during a test signal.

back contact Ta and front contact Tb. These contacts are actuable by a cam CA which is driven is driven by motor M2. Normally the motor M2 is maintained energized in circuit LH, Ta, M2, ALT, 801, LG. The current flow in the circuit is enough to drive the motor M2 and the cam CA. Periodically, say at intervals of an hour. the cam CA momentarily opens Ta and closes Tb. This does not stop M2 but Tb momentarily connects ALT directly to LH so that the supply potential is impressed between ALT and LG.

The coils of ARZ, TER, and AR3 are connected between ALT and LG and are energized when ALT is energized. ARZ is a slow pull-in relay, preferably a thermally operated bimetallic relay, and closes its contact ARZa only if ALT is connected directly to LH for a time interval longer than the interval following the closing of Tb during Which the test alarm should sound. AR3 is a slow drop-out relay; once its coil is energized, its contact AR3a pulls in instantaneously; AR3a remains closed for a short time interval after the coil of AR3 is deenergized.

The coil of RA is connected to ALT through rectifier RXZ. This coil is also adapted to be connected to LH through RXI, front contact AR3a of AR3, TERc and CRd. The coil of RA is also shunted by capacitor C2 which is charged when the coil is energized. C2 prevents RA from dropping out for a predetermined interval after the coil of RA is energized and the energizing current interrupted. A signal lamp 71 is adapted to be connected between LH and LG through RAa and CR0 and a resistor RE7. This lamp is energized during an actual The coil of AR is adapted to be connected between LH and LG through RAb and AR is actuated when RA is actuated to set the alarm Unit for test so that the nonalarming signal is sounded on HOA and the alarm signal on HOT.

The Self-Testing Unit also includes a Test Radiator which is actuable by $01 when ALT is directly connected to LH. This Test Radiator may be a lead ball containing a radioactive material in a cavity (or a neutron source or other source in certain situations). The ball has an opening communicating with the radioactive material. The opening faces away from the tube GM during standby and is turned towards GM during test. The radiation energizes GM producing current pulses which energize PH and TU during test.

A push button PB is provided so that the attendant may connect ALT directly to LH for manual test.

StandbyFI G. 1

During standby power supplies LH, 5, '7 and 9 are energized so that the apparatus is in condition to operate. GM is subjected only to the normal radiation in the protected region and this is too small to energize PH. TU and CR are then'deenergized, M1 is deenergized and there are no signals from HOA or HOT. AR is deenergized and the system is set to reproduce the alarm on HOA.

Self-Testing--FIG. 1

During self-testing Tb is momentarily closed energizing ALT. TER is instantaneously actuated scaling in ALT through TERd and CRd. The motor M2 continues to rotate because of its inertia reopening Tb and reclosing Ta but ALT remains connected to LH.

TERb is opened and TERa closed so that the anode circuit of TU is supplied from the lower voltage 7. TERc opens maintaining open the circuit LH, CRd, TERc, ARSa, RXI, RA, LG.

RA is also actuated opening RAa and closing 'RAb. AR is actuated setting the Alarm Unit for test. ARS is actuated conditioning RA to be maintained actuated through AR3a and RXl for as long as AR3 remains closed after ALT is denergized.

S01 is energized actuating the test radiator. plies pulses of current at a high rate to IN, breaking .down GL1 and energizing PH and TU. CR is actuated GM supclosing CRa to energize the alarm signal lights. CRc is also closed to energize M1. HOA reproduces the nonalarming signal and HOT the alarm signal. The whole system is thus checked. CRd is also opened breaking the sealing circuit for ALT.

ARZ becomes denergized before its contact ARZa closes. TER is deenergized opening TERd to break the sealing circuit until the next test. TERa is opened deenergizing TU and TERb closes resetting TU on the higher anode voltage. TERc closes.

When TU is deenergized, CRd closes. AR3 remains actuated after ALT is deenergized and then drops out. RA is maintained energized until AR3a drops outs. Sufficient time is thus afforded for the Self-Testing Unit to produce a signal and reset itself. Ultimately AR3 drops out and RA is deenergized so that the Self-Testing Unit is reset.

If TU failed before or during the test CR would not be actuated. In this case ALT would remain connected to LH until AR2 would be actuated actuating the secondary alarm.

Alarm-FIG. 1

In the event of excessive radiation on the protected area GM produces pulses of current at a high rate energizing TU. AR is not now actuated so that the alarm is produced on HOA and all personnel warned. Very high intensity radiation would prevent the usual deionization which occurs between pulses and pulsing would cease; however current would flow continuously to charge IN and produce an alarm. Thus the apparatus is not subject to jamming.

FIG. 3

FIG. 3 shows a modified Detector Unit. This Unit is similar to the Unit shown in FIG. 1 including tube GM, network IN, the discharge device GL1 and the photosensitive device PH. The Unit also includes a transistor TR having a base 81, an emitter 83 and a collector 85. The Unit also includes a lamp $7. The transistor TR is blocked by bias BAI connected between its emitter 83 and base 81. The collector 85 is connected to the negative pole 91 of a low voltage direct-current supply through the lamp 87. With TR blocked the lamp S7 is deenergized. The device PH is connected between the base 31 and the negative pole 93 of a suitable supply. With the device PH deenergized 93 is in eflect disconnected from the base 81.

When GM is suificiently energized to break down GL1, the base 81 is rendered electrically negative by the supply 93 acting through PH. Current then flows through 87 maintaining PH energized independently of GM. In addition, a relay such as CR is actuated to produce the necessary signalling.

FIG. 4

In the apparatus shown in FIG. 4 the converter shown in FIG. 2 is applied to the detection of ionization in in water W such as may be produced by-a slight content of minerals. Electrodes I01 and 163 immersed in the water W are connected preferably to a direct-current supply having poles and 107 through a network including a capacitor C3 shunted by a high discharging resistor RE7A, discharge device GL1 having a critical breakdown voltage is connected across C3. On the presence of critical ionization in W, C3 is suiiiciently charged to break down GL1. PHS is energized producing a desired signal.

While preferred embodiments of this invention have been disclosed herein, many modifications thereof are feasible. This invention then is not to be restricted except insofar as is necessitated by the spirit of the prior art.

I claim as my invention:

1. Fail-proof radiation detection apparatus including means responsive to radiation to be detected for producing current on the incidence of radiation thereon, a capacitor, means connecting said current-producing means and said capacitor in an electrical integrating cirwit to integrate said current, a gaseous discharge device in which a luminescent discharge is produced when a potential exceeding a predetermined firing potential is impressed thereon, means connecting said capacitor to said device to impress the potential of said capacitor on said device, light sensitive means only in light receiving relationship with said device but electrically insulated therefrom, and signalling means connected to said sensitive means in a relatively low impedance circuit in which the impedances are ofthe order of thousands of ohms rather than millions of ohms to produce a signal when said device becomes luminescent.

2. A radioactivity alarm system comprising detecting apparatus including a radioactivity detector, amplifying means connected in amplifying relationship with said detector, and an alarm-signal producer connected to said amplifying means to be actuated by said amplifying means on the detection of dangerous radioactivity by said detector, a non-a1arming signal, checking means connected to said apparatus and to said non-alarming signal and periodically actuable to cause said detector, amplifier and alarm-signal producer to operate in the same way as they do when detecting said dangerous radioactivity; said checking means including means, actuable when said checking means is periodically actuated, to connect said signal producer in producing relationship with said nonalarming signal and said amplifier so that said producer produces said non-alarming signal in lieu of an alarm signal.

3. The method of checking a radiation detecting system at reasonable intervals, said system including a record having impressed thereon an alarm signal, a second record having impressed thereon a non-alarming signal, a high output sound reproducer, and low-output sound reproducer, the said method comprising normally maintaining said first record connected in reproducing relationship with said high-output sound reproducer, during each of said intervals connecting said first record in reproducing relationship with said low-output sound reproducer, and said second record in reproducing relationship with said high-output sound reproducer, and causing said records to be reproduced respectively by said reproducers during said last-named interval.

4. A radiation alarm system comprising a first-record having impressed thereon an alarm signal, a second record having impressed thereon a non-alarming signal, a high-output sound reproducer, a low-output sound reproducer, and selectively actuable switch means for selectively connecting said first record in sound reproducing relationship with said high-output reproducer or both said first record in sound reproducing relationship with said low-output reproducer and second record in sound reproducing relationship with: said high-output reproducer.

5. A radiation alarm system comprising first means when actuated for producing an alarm signal at a high sound level, second means connected in alarm-signal deriving relationship to said first means when actuated for producing said alarm signal at a low sound level, third means connected in signal actuation relationship with said first means when actuated for producing a nonalarming signal at said high sound level, means connected to said first means responsive to a predetermined condition in a predetermined region for actuating said first means to produce said alarm signal at said high level, and system checking means connected to said second and third means and actuable to actuate said second and third means substantially simultaneously to produce said alarm signal at said low level and said non-alarming signal at said high level.

6. A radiation alarm system comprising first means when actuated for producing an alarm signal at a high sound level, second means connected in alarm signal deriving relationship to said first means when actuated 8 for producing said alarm signal at a low sound level, third means connected in signal actuation relationship with said first'means when actuated. for producing a nonalarming signal at said high sound level, means connected to said first means responsive to a predetermined condition in a predetermined region for actuating said first means to produce said alarm signal at said high level, and system checking means connected to said second and third means and actuable periodically to actuate said second and third means substantially simultaneously to produce said alarm signal at said low level and said non-alarming signal at said high level for a time interval of a predetermined duration.

7. The method of checking a detecting system at reasonable intervals, said system including first means when conditioned actuable by a predetermined condition in a predetermined region to produce an alarm signal at a high sound level, second means connected to said first means when actuated for producing said alarm signal at a low sound level, and third means connected to said first means when actuated for producing a nonalarrning signal at said high sound level, the said method comprising normally maintaining said first means conditioned to be actuable by said predetermined condition to produce said alarm signal; and during each of said intervals actuating for a predetermined interval both said second means to produce said alarm signal at said lowlevel and said third means to produce said non-alarming signal at said high level,

8. A radiation alarm system comprising first means when actuated for producing an alarm signal at a high sound level, second means. connected in alarm signal deriving relationship to said first means when actuated for producing said alarm signal at a low sound level, third means connected in signal-actuation relationship with said first means when actuated for producing a nonalarming signal at said high sound level, means connected tosaid first means responsive to a predetermined condition in a predetermined region for actuating said first means to produce said alarm signal at said high level, system checking means connected to said second and third means and actuable to actuate said second and third means substantially simultaneously to produce said alarm signal at said low level and said non-alarming signal at said high level, and means connected to. said system checking means for. producing a signal on the failure of said system checking means to actuate said second and third means a predetermined time interval after said checking means is actuated.

9. A converter including voltage-producing storing means, a. lightemitting discharge device having a critical breakdown voltage, means connecting said device and said storing means. so that the voltage of said storing means is impressed on said device, photoelectric means, a normally deenergized auxiliary light, emitting device capable of emitting light when energized, means mounting said photoelectric means in light receiving relationship both with said discharge device and with said auxiliary device, and means connected to said auxiliary device and responsive to the energization of said photoelectric means by light from said discharge device for energizing said auxiliary device.

10. A converter including voltage-producing storing means, a light emitting discharge device having a critical breakdown voltage, means connecting said device and said storing means so that the voltage of said storing means is impressed on said device, photoelectric means, a normally deenergized auxiliary light emitting device capable of emitting light when energized by current transmitted therethrough, means mounting said photoelectric means in light receiving relationship both with said discharge device and with said auxiliary device, a transistor, means connecting said photoelectric means in controlling relationship with said transistor, said last-named means maintaining said transistor non-conducting when said photoelectric means is deenergized and conducting when said photoelectric means is energized by light impinging thereon, and means connecting said transistor in current transmitting relationship to said auxiliary device so that when said transistor is conducting it transmits current through said auxiliary device;

11. Fail-proof radiation detection apparatus including means responsive to radiation to be detected for producing currenton the incidence of radiation thereon, said current-producing means including terminals between which a high electrical potential of the order of 1000 volts is impressed, a capacitor, means connecting said currentproducing means and said capacitor inan electrical integrating circuit to integrate said current, a gaseous discharge device in which a luminescent discharge is produced when a potential exceeding a predetermined firing potential is impressed thereon, means connecting said capacitor to said device to impress the potential of said capacitor on said device, light sensitive means electrically insulated from said high potential but in light receiving relationship with said device, signalling means connected to said sensitive means to produce a signal when said device becomes luminescent and an energizing circuit for said light-sensitive means and signalling means including terminals between which an electrical potential of the order of 100 volts is to be impressed.

12. Fail-proof radiation detection apparatus including means responsive to radiation to be detected for producing current pulses on the incidence of radiation'of moderate intensity thereon and producing continuous current on the incidence of high intensity radiation thereon, a capacitor, means connecting said current-producing means and said capacitor in an electrical integrating circuit to integrate both said current pulses and said continuous current, a gaseous discharge device in which a luminescent discharge is produced when a potential exceeding a predetermined firing potential is impressed thereon, means connecting said capacitor'to said device to impress the potential of said capacitor on said device, said potential on said capacitor becoming equal to said firing potential both. on theoccurrence of said current pulses at a sufiiciently high rate responsive to correspond to radiation of moderate but dangerous intensity and also on the occurrence of said continuous current, light sensitive means in light receiving relationship with said device but electrically insulated therefrom, and signalling means connected to said sensitive means to produce a signal when said device becomes luminescent.

13. Fail-proof radiation detection apparatus including means responsive to radiation to be detected for producing current pulses on the incidence of radiation of 10 producing means and said capacitor in an electrical integrating circuit to integrate said current, a gaseous dis charge device in which a luminescent discharge is produced when a potential exceeding a predetermined firing potential is impressed thereon, means connecting said capacitor to said device to impress the potential of said capacitor on said device, said potential on said capacitor becoming equal to said firing potential both on the occurrence of said current pulses at a sufficiently high rate responsive to correspond to radiation of moderate but dangerous intensity and also on the occurrence of said continuous current, light sensitive means electrically insulated from said high potential but in light receiving moderate intensity thereon; and producing continuous I current on the incidence of high-intensity. radiation thereon, said current-producing means including terminals between which a high potential of the order of 1000 volts is impressed, a capacitor, means connecting said currentrelationship with said device, signalling means connected to said sensitive means to produce a signal'when said device becomes luminescent and an energizing circuit for said light sensitive means and signalling means including terminals between which an electrical potential of the order of volts is to be impressed.

14. A radiation alarm system comprising a first record having impressed thereon an alarm signal, a second rec 0rd having impressed thereon a non-alarming signal, a high-output sound reproducer, a low-output sound reproducer, a relay having back-contact means and frontcontact means, means including said back-contact means connecting said first record in reproducing relationship 1. with said high-output reproducer, and means connected to said front-contact means for connecting both said first record in sound reproducing relationship with said lowoutput reproducer and second record in'sound reproducing relationship with said high-output reproducer.

References (lifted by the Examiner UNITED STATES PATENTS 2,03 6,072 3/36 Mutscheller 250-83.6 2,037,924 4/36 Rentschler 25083.6 2,230,435 2/41 Potts 250233 X 2,302,874 11/42 Lion 250-833 2,408,589 10/46 Wells 250-217 2,582,850 l/52 Rose 250211 2,648,015 8/53 Greenfield et a1 25083.6 2,831,981 4/58 Watts 250--211 2,944,152 7/60 Johnson et al 250-836 2,947,874 8/60 Tomlinson 250 -208 2,963,588 12/60 Wilson 25083.6 2,965,760 12/60 Crump 250--83.6 2,977,505 3/61 Smith 250-209 X 2,982,857 5/61 Clarke 25083.6 2,984,746 5/61 Speh et a1, 250-83.6 3,041,457 6/62 Wall 250-200X 3,042,807 7/62 Vize 250-213 RALPH G. NILSON, Primary Examiner. ARTHUR GAUSS, Examiner. 

1. FAIL-PROOF RADIATION DETECTION APPARATUS INCLUDING MEANS RESPONSIVE TO RADIATION TO BE DETECTED FOR PRODUCING CURRENT ON THE INCIDENCE OF RADIATION THEREON, A CAPACITOR, MEANS CONNECTING SAID CURRENT-PRODUCING MEANS AND SAID CAPACITOR IN AN ELECTRICAL INTEGRATING CIRCUIT TO INTEGRATE SAID CURRENT, A GASEOUS DISCHARGE DEVICE IN WHICH A LUMINESCENT DISCHARGE IS PRODUCED WHEN A POTENTIAL EXCEEDING A PREDETERMINED FIRING POTENTIAL IS IMPRESSED THEREON, MEANS CONNECTING SAID CAPACITOR TO SAID DEVICE TO IMPRESS THE POTENTIAL OF SAID CAPACITOR ON SAID DEVICE, LIGHT SENSITIVE MEANS ONLY IN LIGHT RECEIVING RELATIONSHIP WITH SAID DEVICE BUT ELECTRICALLY INSULATED THEREFROM, AND SIGNALLING MEANS CONNECTED TO SAID SENSITIVE MEANS IN A RELATIVELY LOW IMPEDANCE CIRCUIT IN WHICH THE IMPEDANCES ARE OF THE ORDER OF THOUSANDS OF OHMS RATHER THAN MILLIONS OF OHMS TO PRODUCE A SIGNAL WHEN SAID DEVICE BECOMES LUMINESCENT. 